MTX Audio 421D ❼ ❺ ❹ ❻ ❶ ❷ ❸, ❽ ❺ ❹, ❽❸ ❷ ❶ ❹ ❻ ❺ ❾, Input Panel Layout, Wire harness color codes

POWER AMPLIFIER OWNER’S MANUAL

1.Gain Controls – These controls are used to match the input sensitivity of the amplifier to the particular source unit that you are using. The controls are factory set to 1Vrms.

2.Thunder EQ – This equalization circuit is used to enhance the low frequency response of the vehi- cle’s interior. With up to 18dB of boost and centered at 40Hz, the Bass EQ can be adjusted to meet your own personal taste.

3.Frequency Control – This control is continuously adjustable from 40Hz through 200Hz at 24dB per octave. Factory setting is at 40Hz.

4.RCA Input Jacks – RCA type input jacks for use with source units that have RCA or Line Level Outputs. A source unit with a minimum output level of 200mV is required for proper operation. However, this input will accept levels up to 8Vrms.

5.EBC 2 – The EBC, or Electronic Bass Control, allows a remote bass control to be adjusted from the dri- ver’s seat. If the optional EBC is installed, the bass level will be able to be adjusted to overcome noise and other interference. With EBC 2 multiple amplifiers can be controlled.

6.RCA-Output Jacks – These RCA outputs allow for a signal to be sent to other amplifiers in a daisy-chain configuration. The RCA outputs also allow for multiple bass amplifiers to be level controlled using one EBC.

7.Speaker Level Inputs – This input will allow the Thunder421D and 801D to operate from source units with speaker-level outputs. Output speaker leads from the source unit should be tied directly to the wire har- ness provided with the amplifier.

Wire harness color codes:
Grey / Black = Source units right negative (-)	White / Black = Source units left negative (-)
Solid Grey = Source units right positive (+)	Solid White = Source units left positive (+)

With the Smart-Engage™ auto-turn circuit, a remote turn-on wire is not necessary when connecting the speaker-level input wire harness to a high powered source unit. The amplifier will automatically turn on when music is received.

8.Compression Circuit – This new circuit, found on the Thunder801D and Thunder1501D, prevents the amplifier from going into clipping, even at high SPL levels. The compression circuit allows the listener to play the amplifier at high volume levels, yet protects the speakers against the potential damage that can occur during dynamic musical passages. The circuit is switchable on/off, for those SPL competitors who run their amplifiers into clipping on purpose. Warning: Damage to speakers may occur when the com- pression circuit is in the off position.

9.Phase Select Switch (Thunder1501D) – The Amp Phase Select switch allows you to invert the phase by 180 degrees at the output. This switch does not affect the phase of the RCA Line Outputs.

6

Input Panel Layout

❼ ❺ ❹ ❻ ❶ ❷ ❸

❽ ❺ ❹	❻ ❶ ❷ ❸
❼

❽❸ ❷ ❶ ❹ ❻ ❺ ❾

7